(a) Field of the Invention
The present invention relates to a rectifier filter control device for a power supply, and more particularly to a rectifier filter control device which Improves availability factor of electric energy, which, moreover, places two electronic switches in off states in advance to a reverse current flow back into the rectifier filter circuit, thereby preventing reverse current flow from burning out the two electronic switches.
(b) Description of the Prior Art
Referring to FIG. 3, which shows a rectifier filter circuit (current doubler) of prior art that uses two diodes CR3, CR4 to function as rectifiers, signal output terminals A1, A2 of a rectangular wave power generator A actuated by a logic IC (integrated circuit) D output a logic signal of positive half cycle (positivity duly cycle) at different time sequences to contact points O1 and another receiving point O2 respectively, and change produced in the positive and negative electrodes B1, B2 of a transformer B at different time sequences enables the diode CR4 or the diode CR3 to conduct electricity at different time sequences. However, when the diodes CR3 and CR4 are forward conducting electricity, a forward voltage drop still exists between the positive and negative electrodes B1, B2, thereby resulting in consumption of output electric energy, wherein power loss P=0.7V×ICR3 (CR3 current) or P=0.7V×ICR4 (CR4 current). Hence, in order to resolve shortcomings of the aforementioned prior art, another improved circuit (Sync Rectifier Current doubler) is used. Referring to FIG. 4, wherein the IC D is used to output a signal to a rectifier filter circuit, which has a primary characteristic in that two electronic switches SW1, SW2 are connected to the two diodes CR4, CR3 respectively, and component structure of the two electronic switches SW1, SW2 are field effect transistors (FET), which are able to reduce voltage difference between the positive and negative electrodes of the diodes CR3, CR4 when the two electronic switches SW1, SW2 are in on states, thereby increasing efficiency of electric energy output. However, a shortcoming of this prior art arises when power operating cycle is too small, whereby a reverse current flow that flows back to the electronic switches SW1, SW2 because of certain factors (for instance, improper use or connection), and when current value of this reverse current flow exceeds current withstand value of the electronic switches SW1, SW2, then burnout of the electronic switches SW1, SW2 results.